The present invention relates to a lightweight refractory substance having improved heat resistance. More particularly, the present invention relates to a lightweight refractory that withstands repeated heating and cooling without damage and which is suitable for use not only in firing auxiliaries such as trays and plinths that are employed to support the members being fired to produce a variety of ceramic products such as ceramic electronic components (e.g. ceramic capacitors, alumina substrates, ferritic devices, thermistors and varistors), ceramic sliding materials and ordinary potteries, but also in heat-shielding plates and supports for heating elements used in various ceramic furnaces.
The firing auxiliaries and ceramic furnace components mentioned above must exhibit not only high enough heat resistance to withstand repeated heating and cooling cycles but also varying degrees of mechanical strength that suit specific uses. At the same time, it is desired that they display low levels of heat storage per unit of volume and are lightweight in order that energy costs can be reduced and production rates raised by reducing the level of thermal energy consumed during furnace operations and shortening the time required to achieve heating and cooling. In particular, firing auxiliaries are strongly desired to be lightweight for the specific purpose of facilitating conveyance and other aspects of handling.
A lightweight refractory that has been developed to meet these demands is described in Unexamined Published Japanese Patent Application No. 88378/84. This refractory is produced by adding 0.5-10 parts by weight of amorphous silica to 100 parts by weight of an aggregate made of 90-50 wt % of the powder of a refractory raw material such as alumina- or mullite-based material and 10-50 wt % of the fibers of a refractory material such as alumina- or mullite-based material, shaping the mixture, and firing the shaped mixture at 1,450.degree.-1,600.degree. C. However, the lightweight refractory produced by this method has a high alumina content and experiences great thermal expansion. It is therefore unsatisfactory in terms of resistance to spalling and creep.